Description of the methods used to generate the image is available here.

“To map the network of citations, we imported the data into a Microsoft Excel spreadsheet running a social-network analysis extension called NodeXL. Citations erroneously discarded by Sitkis were entered manually into this spreadsheet.

To reveal a core network of citations among the primary authors, we filtered to exclude all connections where the scientists cited one another’s work less than four times, and drew the diagram so that its elements reflected the number and strength of the remaining links: the more citations, the larger the arrows; the more incoming links, the larger the node representing that scientist. Finally, we adjusted the layout manually to most clearly show any differences in the network based on author location.

There were 43 scientists in the network, 24 from the US and 19 from elsewhere. All but two researchers – one in the US and one in Germany – connected to Shinya Yamanaka of Kyoto University in Japan, the pioneer of cellular reprogramming, but non-US scientists had no other links among themselves. The US side of the diagram showed a richer network of links, with 33 connections among 17 scientists. Seven of the non-US scientists, including Yamanaka, connected with US-based researchers, making a total of 16 links. However, no scientist working in the US linked to any non-US scientist other than Yamanaka.” [Link]

Hi Marc, saw this too and was thinking about own use of nodexl – any views on their layout that gives appearance of a radial layout, with original position of central nodes revealed by the gaps in outer circle of nodes? Do you think that helps?